On the basis of present knowledge, it appears that atherosclerosis can be prevented and possibly even treated by correcting hyperlipidemia. The practicability of decreasing blood lipids in animals and man, either by dietary manipulation, by certain chemotherapeutic agents, and even by a surgical procedure, has been adequately demonstrated. Polyunsaturated dietary fat has been shown to have a hypocholesteremic effect in animals and in man however there is a great deal of controversy as to its mechanism of action. Although various sites of action have been proposed, no single mechanism has been shown to apply in all situations. The objective of the present proposal is to investigate the effect of saturated and polyunsaturated dietary fat on plasma cholesterol levels and on the secretion of biliary lipids. These investigations will involve the use of an experimental animal model, the minipig, with a modified Baldwin T-tube catheter positioned in the common bile duct. This will enable long term studies of bile flow and composition while keeping the enter ohepatic circulation intact. The study of cholesterol and its end products, in bile acids, before they are changed into other metabolites in the gastrointestinal tract may provide more accurate information regarding the mechanisms by which dietary fats influence plasma cholesterol levels.